1. Field of the Invention
The present invention relates to the field of optical lenses, and more particularly to a four-piece imaging lens module capable of providing smaller chief ray angle of light sensor, high definition and higher yield rate.
2. Description of the Prior Art
At present, digital carriers having a lens module, which has a function of photo-taking or filming, will increase its additional value and will attract young group. Some portable digital carriers such as digital cameras, mobile phones, NB, video players or Webcams are also provided with such lens modules. However, these portable digital carriers are small in size, thus imposing some limitations on the lens module. That is, the length of the lens module is inevitably limited.
Besides, the competitive market also results in the reduction of profit. In order to obtain product differentiation, the digital carriers are further provided with high level lens modules for marketing purposes. That is, the cost of producing the lens modules should be cut down, and the quality of the lens modules should be improved.
For the limitation and the purposes above, lens which has one or two aspheric surface(s) is used as an alternative. However, it is used only in two-piece and three-piece lens modules. To achieve the requirement of high-definition, four-piece lens module is still irreplaceable.
In conventional four-piece lens module, the second lens has a convex surface on the object side. The third lens has a convex surface on the image side. The fourth lens has a convex surface on the object side around the light axis of the fourth lens. However, such four-piece lens module is difficult to be produced, so that the yield rate can hardly be improved. In addition, the lens module is also difficult to provide a smaller chief ray angle for light receiver or light sensor.
As such, the present invention is arisen to obviate or at least mitigate the above mentioned disadvantages.